Theoretical studies on effects of hydrogen bonds attaching to cysteine ligands on 4Fe‐4S clusters

Abstract

Abstract The effect of hydrogen bonds attaching to sulfur atoms of cysteine ligands on 4Fe‐4S cluster is examined by using UB3LYP method. Calculated results indicate that an existence of the hydrogen bonds scarcely changes SOMO‐SUMO gap, shapes of Kohn‐Sham orbitals, and magnetic interactions between Fe ions, although it stabilizes Kohn‐Sham orbital energies of SOMO and SUMO about 1.0 eV. And they also make a reduced state stable in comparison with an oxidized state. In addition, the point charges of +0.1 e ( e : elementary electric charge) at the position of the hydrogen atoms give almost same results to the hydrogen bonds quantitatively. The results suggest that a positive environment from the hydrogen bonds around the clusters is important for a redox potential of 4Fe‐4S clusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008